1. Field of the Invention
The present invention relates to a power breaker system which is used in a main circuit of a distributor. More particularly, it relates to a power breaker system which selectively breaks feeder breakers connected to a plurality of load circuits by fault current limiting function and a short timing delay function of breaking operation of a main breaker.
2. Description of the Prior Arts
Heretofore, power breaker systems shown in FIGS. 1 and 2 have been known.
In the power breaker system of FIG. 1, a main breaker ACB is connected between a power source terminal (1) and a plurality of branch load circuits (2.sub.1) to (2.sub.n) which respectively comprises feeder breakers B.sub.1 to B.sub.n, electromagnetic switches MS.sub.1 to MS.sub.n and loads L.sub.1 to L.sub.n such as induction motors.
In the circuit, when a short-circuit fault is caused at a point F.sub.1 in the branch load circuit 2.sub.1, it is necessary to break only the fault circuit and to continue the feeding to the other circuits 2.sub.2 to 2.sub.n, and accordingly, the main breaker ACB has short timing delay function to actuate the feeder breaker B.sub.1 before actuating the main breaker ACB so as to attain the selective breaking.
The selective breaking can be attained by the breaker system having such structure, however the system has not a function for limiting fault current, whereby the feeder breaker is broken when excess fault current is passed. Accordingly, it has been serious problem to consider a protection of a feeder breaker.
On the other hand, in the other conventional system of FIG. 2, a current limiting fuse F having large break capacity is used instead of the main breaker ACB to give said current limiting function. That is, the current limiting fuse F is fused by passing excess energy. When a fault current A.sub.1 is passed as shown in FIG. 3, the fuse is fused at the point A.sub.2 by storing energy E (hatching part) in the fuse F. Accordingly, the feeder breaker is protected by the fuse F when the energy for fusing the fuse is lower than a maximum energy of the feeder breaker. In such circuit system, a power distribution to all of circuits is interrupted after fusing the fuse F (point P.sub.1 in FIG. 3) and the selective breaking can not be attained even though the back-up of the feeder breaker can be expected.